Technical Field
The present disclosure relates to a light-emitting device including a light-emitting element and a wavelength conversion member and to an image display including the light-emitting device.
Background Art
There has been recently developed a light-emitting device that includes a combination of (i) a semiconductor light-emitting element such as a light-emitting diode (LED) and (ii) a wavelength conversion member (for example, a member in which phosphor particles are dispersed into a resin) that converts excitation light from the semiconductor light-emitting element into phosphorescence. The light-emitting device has a small size and has the advantage of consuming lower power than an incandescent light bulb. Accordingly, the light-emitting device is practically employed as a light source for a variety of image displays or for illumination devices.
A general type of such a light-emitting device employed includes a combination of a blue LED and a yellow phosphor. A Ce-activated yttrium aluminum garnet (YAG) phosphor is widely employed for the yellow phosphor because of a high luminous efficiency.
In the case of employing the light-emitting device as an image display, the color reproduction range of the image display widens as the emission spectral half width of the phosphor decreases. However, the emission spectral half width of the Ce-activated YAG phosphor is comparatively large, about 100 nm. Therefore, the width of the color reproduction range is insufficient when a semiconductor light-emitting device employing the Ce-activated YAG phosphor for the yellow phosphor is configured as a liquid crystal backlight of the image display.
Specifically, the image display can cover almost the entire standard red green blue (sRGB) color gamut that is employed in a cathode ray tube (CRT). However, the coverage remarkably decreases with respect to the Adobe RGB color gamut that is employed in a wide color gamut liquid crystal display.
More specifically, when the semiconductor light-emitting device employing the Ce-activated YAG yellow phosphor is employed as the liquid crystal backlight of the image display, the color gamut of the image display has a coverage of about 70% with respect to the Adobe RGB color gamut. Therefore, the semiconductor light-emitting device is not suitable for use in the wide color gamut liquid crystal display.
The sRGB color gamut is defined by a triangle that is formed by three chromaticity points of (CIEx, CIEy)=(0.640, 0.330), (0.300, 0.600), (0.150, 0.060) on the Commission Internationale de l'Eclairage (CIE) 1931 chromaticity coordinate plane.
On the other hand, the Adobe RGB color gamut is defined by a triangle that is formed by three chromaticity points of (CIEx, CIEy)=(0.640, 0.330), (0.210, 0.710), (0.150, 0.060) on the CIE 1931 chromaticity coordinate plane. The Adobe RGB color gamut has a wide green color reproduction range when compared with the sRGB color gamut.
A semiconductor light-emitting device compatible with Adobe RGB and suitable for use as the backlight of the wide color gamut liquid crystal display is configured to employ a combination of two different colored phosphors of a green phosphor and a red phosphor. It is desirable that the emission spectral half widths of those phosphors are narrow.
In International Publication No. WO 2009/110285 (published on Sep. 11, 2009) and Japanese Unexamined Patent Application Publication No. 2010-93132 (published on Apr. 22, 2010), there is disclosed a semiconductor light-emitting device that employs a combination of an Eu-activated β-SiAlON phosphor and an Mn4+-activated fluoride complex as a phosphor. According to the combination when configured in the image display, a wide color reproduction range can be realized in comparison with a configuration employing the yellow phosphor as a phosphor.
This results from the fact that the emission spectral half width of the Eu-activated β-SiAlON phosphor and the half width of the Mn4+-activated fluoride complex phosphor are narrower than that of the Ce-activated YAG phosphor. Specifically, the emission spectral half width of the Eu-activated β-SiAlON phosphor is less than or equal to 55 nm. The half width of the Mn4+-activated fluoride complex phosphor is less than or equal to 10 nm.
The emission spectral half width of the Eu-activated β-SiAlON phosphor is less than or equal to 55 nm and is narrower than the emission spectral half width of the Ce-activated YAG yellow phosphor. However, combining the Eu-activated β-SiAlON phosphor with a phosphor having a narrower emission spectral half width can additionally realize an image display having a further wider color reproduction range.
In Japanese Unexamined Patent Application Publication No. 2011-142336 (published on Jul. 21, 2011), there is disclosed a configuration that includes a combination of a blue LED and two types of quantum dot phosphors emitting green and red light. However, in the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2011-142336 (published on Jul. 21, 2011), the red light emitting quantum dot phosphor absorbs the green light of the green light emitting quantum dot phosphor. This poses a problem in that the luminous efficiency of the light-emitting device decreases remarkably.
In Japanese Unexamined Patent Application Publication No. 2012-163936 (published on Aug. 30, 2012), Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2013-519232 (published on May 23, 2013), and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2013-534042 (published on Aug. 29, 2013), there is disclosed a configuration that employs a combination of a quantum dot phosphor and the Mn4+-activated fluoride complex phosphor as the phosphor dispersed into the wavelength conversoin member. The Mn4+-activated fluoride complex phosphor does not absorb green light, unlike the quantum dot phosphor. Therefore, according to the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2012-163936 (published on Aug. 30, 2012), Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2013-519232 (published on May 23, 2013), and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2013-534042 (published on Aug. 29, 2013), the problem of the red light emitting phosphor absorbing the green light emitted by the green light emitting phosphor is resolved.
However, a configuration suitable for realizing the image display having a wide color reproduction range with the light-emitting device including a combination of the Mn4+-activated fluoride complex phosphor and the quantum dot phosphor is not disclosed in any of Japanese Unexamined Patent Application Publication No. 2012-163936 (published on Aug. 30, 2012), Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2013-519232 (published on May 23, 2013), and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2013-534042 (published on Aug. 29, 2013).